Organic electroluminescent devices

Abstract

The present invention relates to electronic devices, in particular organic electroluminescent devices, which comprise compounds of the formula (1), and to the corresponding compounds and to the use thereof in organic electroluminescent devices.

The invention claimed is: 
     
       1. An electronic device comprising at least one compound of the formula (1) or formula (39) 
       
         
           
           
               
               
           
         
         where the following applies to the symbols and indices used: 
         A-B and D-E are each, identically or differently on each occurrence, a unit of the following formula (2), (3), (4), (5) or (6): 
       
       
         
           
           
               
               
           
         
         where the dashed bond in each case represents the link to Z and B or D; 
         and 
         Z is, identically or differently on each occurrence, N—R 2 , O or S; 
         or 
         A-Z and B-Z are each, identically or differently on each occurrence, a unit of the following formula (7) and q=0, 
       
       
         
           
           
               
               
           
         
         the dashed bond represents the linking of the unit to the compound of the formula (1), where the nitrogen is linked to the group Y; 
         Y is on each occurrence, identically or differently, P(═O), P(═S), P, As(═O), As(═S), As, Sb(═O), Sb(═S), Sb, Bi(═O), Bi(═S) or Bi; 
         Ar is on each occurrence, identically or differently, an aromatic or heteroaromatic ring system having 5 to 60 aromatic ring atoms, which may be substituted by one or more radicals R 1 ; 
         Ar 1  is on each occurrence, identically or differently, an aryl or heteroaryl group having 5 to 18 aromatic ring atoms, which may be substituted by one or more radicals R 1 ; 
         X is on each occurrence, identically or differently, CR 1  or N; 
         L is a single bond or a divalent, trivalent or tetravalent group; 
         R 1  is selected on each occurrence, identically or differently, from the group consisting of H, D, F, Cl, Br, I, CN, NO 2 , N(R 3 ) 2 , C(═o)R 3 , a straight-chain alkyl, alkoxy or thioalkyl group having 1 to 40 C atoms or a branched or cyclic alkyl, alkoxy or thioalkyl group having 3 to 40 C atoms or an alkenyl or alkynyl group having 2 to 40 C atoms, each of which may be substituted by one or more radicals R 3 , where one or more non-adjacent CH 2  groups may be replaced by R 3 C═CR 3 , C≡C, Si(R 3 ) 2 , Ge(R 3 ) 2 , Sn(R 3 ) 2 , C═O, C═S, C═Se, C═NR 3 , P(═O)(R 3 ), SO, SO 2 , NR 3 , O, S or CONR 3  and where one or more H atoms may be replaced by D, F, Cl, Br, I, CN or NO 2 , an aromatic or heteroaromatic ring system having 5 to 60 aromatic ring atoms, which may in each case be substituted by one or more radicals R 3 , an aryloxy or heteroaryloxy group having 5 to 60 aromatic ring atoms, which may be substituted by one or more radicals R 3 , or a combination of these systems, where two or more adjacent substituents R 1  may optionally form a monocyclic or polycyclic, aliphatic, aromatic or heteroaromatic ring system, which may be substituted by one or more radicals R 3 ; 
         R 2  is selected on each occurrence, identically or differently, from the group consisting of a straight-chain alkyl group having 1 to 40 C atoms or a branched or cyclic alkyl group having 3 to 40 C atoms, each of which may be substituted by one or more radicals R 3 , where one or more non-adjacent CH 2  groups may be replaced by R 3 C═CR 3 , C≡C or C═O and where one or more H atoms may be replaced by D, F, Cl, Br, I, CN or NO 2 , an aromatic or heteroaromatic ring system having 5 to 60 aromatic ring atoms, which may in each case be substituted by one or more radicals R 3 , or a combination of these systems; R 1  and R 2  which are adjacent to one another in the 1,2-position may optionally form a monocyclic or polycyclic, aliphatic, aromatic or heteroaromatic ring system, which may be substituted by one or more radicals R 3 ; 
         R 3  is selected from the group consisting of H, D, F, CN, an aliphatic hydrocarbon radical having 1 to 20 C atoms, an aromatic or heteroaromatic ring system having 5 to 30 aromatic ring atoms, in which one or more H atoms may be replaced by D, F, Cl, Br, I or CN, where two or more adjacent substituents R 3  may form a mono- or polycyclic, aliphatic, aromatic or heteroaromatic ring system with one another; 
         n, t is 1 to 10; 
         m is 1 if L is a single bond or a divalent group, or is 2 if L is a trivalent group, or is 3 if L is a tetravalent group; 
         q is on each occurrence, identically or differently, 0 or 1. 
       
     
     
       2. The electronic device according to  claim 1 , wherein Ar 1  stands, identically or differently on each occurrence, for an aryl or heteroaryl group having 5 to 14 aromatic ring atoms. 
     
     
       3. The electronic device according to  claim 1 , wherein the compound of the formula (1) is selected from compounds of the formulae (8) to (18): 
       
         
           
           
               
               
           
         
         
           
           
               
               
           
         
         where the symbols and indices used have the meanings indicated in  claim 1 . 
       
     
     
       4. The electronic device according to  claim 1 , wherein the symbol Y stands for P(═O) and the symbol Z stands on each occurrence, identically or differently, for N—R 2 . 
     
     
       5. The electronic device according to  claim 1 , wherein the group Ar stands for an aromatic or heteroaromatic ring system having 5 to 30 aromatic ring atoms, selected from the group consisting of the units of the following formulae (19) to (36), where the dashed bond in each case indicates a link to the group Y in formula (1) or to N in formula (39): 
       
         
           
           
               
               
           
         
         
           
           
               
               
           
         
         
           
           
               
               
           
         
       
     
     
       6. The electronic device according to  claim 1 , wherein R 2  is selected, identically or differently on each occurrence, from the group consisting of an aromatic or heteroaromatic ring system having 5 to 24 aromatic ring atoms, which may in each case be substituted by one or more radicals R 3 . 
     
     
       7. The electronic device according to  claim 1 , wherein the following applies to the symbols and indices:
 Ar 1  is, identically or differently on each occurrence, an aryl or heteroaryl group having 5 to 14 aromatic ring atoms; 
 Y is on each occurrence, identically or differently, P(═O) or P(═S); 
 Z is, identically or differently on each occurrence, N—R 2  if it does not form a ring of the formula (7) with A or B; 
 X stands for CR 1  or N, where a maximum of two symbols X stand for N; 
 Ar is, identically or differently, an aromatic or heteroaromatic ring system having 5 to 30 aromatic ring atoms; 
 q is 0; 
 n is 1, 2, 3 or 4; 
 R 1  is selected, identically or differently on each occurrence, from the group consisting of H, I), F, CN, N(R 3 ) 2 , a straight-chain alkyl or alkoxy group having 1 to 20 C atoms or a branched or cyclic alkyl or alkoxy group having 3 to 20 C atoms or an alkenyl group having 2 to 20 C atoms, each of which may be substituted by one or more radicals R 3 , where one or more non-adjacent CH 2  groups may be replaced by R 3 C═CR 3  or O and where one or more H atoms may be replaced by D or F, an aromatic or heteroaromatic ring system having 5 to 30 aromatic ring atoms, which may in each case be substituted by one or more radicals R 3 , an aryloxy or heteroaryloxy group having 5 to 30 aromatic ring atoms, which may be substituted by one or more radicals R 3 , or a combination of these systems, where two or more adjacent substituents R 1  may optionally form a monocyclic or polycyclic, aliphatic, aromatic or heteroaromatic ring system, which may be substituted by one or more radicals R 3 ; 
 R 2  is selected on each occurrence, identically or differently, from the group consisting of a straight-chain alkyl group having 1 to 10 C atoms or a branched or cyclic alkyl group having 3 to 10 C atoms, each of which may be substituted by one or more radicals R 3 , where one or more H atoms may be replaced by F or D, an aromatic or heteroaromatic ring system having 5 to 30 aromatic ring atoms, Which may in each case be substituted by one or more radicals R 3 , or a combination of these systems; R 1  and R 2  which are adjacent to one another in the 1,2-position may optionally form a monocyclic or polycyclic, aliphatic, aromatic or heteroaromatic ring system, which may be substituted by one or more radicals R 3 ; 
 the other symbols and indices have the meanings indicated in  claim 1 . 
 
     
     
       8. The electronic device according to  claim 1 , wherein the following applies to the symbols and indices used:
 Ar 1  is selected, identically or differently on each occurrence, from the group consisting of benzene, pyridine, pyrimidine, pyridazine, pyrazine, triazine, furan, thiophene, pyrrole, naphthalene, quinoline, isoquinoline, quinoxaline, indole, benzofuran, benzothiophene and carbazole; 
 Y is P(═O); 
 Z is, identically or differently on each occurrence, N—R 2  if it does not form a ring of the formula (7) with A or B; 
 X is, identically or differently on each occurrence, CR 1 ; 
 Ar is an aromatic or heteroaromatic ring system having 5 to 24 aromatic ring atoms, which is built up from in each case one or more of the groups benzene, pyridine, pyrimidine, pyridazine, pyrazine, pyrrole, thiophene, furan, naphthalene, triphenylene, quinoline, isoquinoline, quinoxaline, indole, benzothiophene or benzofuran; 
 q is 0; 
 n is 1 or 2; 
 R 1  is selected, identically or differently on each occurrence, from the group consisting of H, D, F, CN, a straight-chain alkyl group having 1 to 10 C atoms, or a branched or cyclic alkyl group having 3 to 10 C atoms, or an alkenyl group having 2 to 10 C atoms, each of which may be substituted by one or more radicals R 3 , where one or more H atoms may be replaced by D, an aromatic or heteroaromatic ring system having 5 to 12 aromatic ring atoms, which may in each case be substituted by one or more radicals R 3 , or a combination of these systems, where two or more adjacent substituents R 1  may optionally form a monocyclic or polycyclic, aliphatic, aromatic or heteroaromatic ring system, which may be substituted by one or more radicals R 3 ; 
 R 2  is selected on each occurrence, identically or differently, from the group consisting of an aromatic or heteroaromatic ring system having 5 to 24 aromatic ring atoms, which may in each case be substituted by one or more radicals R 3 ; 
 the other symbols and indices used have the meanings indicated in  claim 1 . 
 
     
     
       9. The electronic device according to  claim 1 , wherein the device is selected from the group consisting of organic electroluminescent devices (OLEDs), organic integrated circuits (O-ICs), organic field-effect transistors (O-FETs), organic thin-film transistors (O-TFTs), organic light-emitting transistors (O-LETs), organic solar cells (O-SCs), organic optical detectors, organic photoreceptors, organic field-quench devices (O-FQDs), light-emitting electrochemical cells (LECs), organic laser diodes (O-lasers) and organic plasmon emitting devices. 
     
     
       10. The electronic device according to  claim 3 , wherein the compound of the formula (1) or formulae (8) to (18) is employed as matrix material for fluorescent or phosphorescent emitters and/or as hole-blocking material in a hole-blocking layer and/or as electron-transport material in an electron-transport layer or an electron-injection layer and/or as electron-blocking material or exciton-blocking material in an electron-blocking or exciton-blocking layer and/or as hole-transport material in a hole-transport layer or hole-injection layer. 
     
     
       11. The electronic device according to  claim 10 , wherein the phosphorescent emitter employed is a compound which contains copper, molybdenum, tungsten, rhenium, ruthenium, osmium, rhodium, iridium, palladium, platinum, silver, gold or europium. 
     
     
       12. A compound of the formula (1′) 
       
         
           
           
               
               
           
         
         where the following applies to the symbols and indices used: 
         A-B and D-E are each, identically or differently on each occurrence, a unit of the following formula (2), (3), (4), (5) or (6): 
       
       
         
           
           
               
               
           
         
         where the dashed bond in each case represents the bond to Z and B or D; 
         and 
         Z is, identically or differently on each occurrence, N—R 2 , O or S, with the proviso that both groups Z bonded to the same group Y do not stand for O; 
         or 
         A-Z and B-Z are each, identically or differently on each occurrence, a unit of the following formula (7) and q=0, 
       
       
         
           
           
               
               
           
         
         the dashed bond in formula (7) in each case represents the linking of this unit in the compound of the formula (1), where the nitrogen is linked to the group Y; 
         Y is on each occurrence, identically or differently, P(═O), As(═O), As(═S), Sb(═O), Sb(═S), Bi(═O) or Bi(═S); 
         Ar is on each occurrence, identically or differently, an aromatic or heteroaromatic ring system having 5 to 60 aromatic ring atoms, which may be substituted by one or more radicals R 1 ; 
         Ar 1  is on each occurrence, identically or differently, an aryl or heteroaryl group having 5 to 16 aromatic ring atoms, which may be substituted by one or more radicals R 1 ; 
         X is on each occurrence, identically or differently, CR 1  or N; 
         L is a single bond or a divalent, trivalent or tetravalent group; 
         R 1  is selected on each occurrence, identically or differently, from the group consisting of H, D, F, Cl, Br, I, CN, NO 2 , N(R 3 ) 2 , C(═O)R 3 , a straight-chain alkyl, alkoxy or thioalkyl group having 1 to 40 C atoms or a branched or cyclic alkyl, alkoxy or thioalkyl group having 3 to 40 C atoms or an alkenyl or alkynyl group having 2 to 40 C atoms, each of which may be substituted by one or more radicals R 3 , where one or more non-adjacent CH 2  groups may be replaced by R 3 C═CR 3 , C≡C, Si(R 3 ) 2 , Ge(R 3 ) 2 , Sn(R 3 ) 2 , C═O, C═S, C═Se, C═NR 3 , P(═O)(R 3 ), SO, SO 2 , NR 3 , O, S or CONR 3  and where one or more H atoms may be replaced by D, F, Cl, Br, I, CN or NO 2 , an aromatic or heteroaromatic ring system having 5 to 60 aromatic ring atoms, which may in each case be substituted by one or more radicals R 3 , an aryloxy or heteroaryloxy group having 5 to 60 aromatic ring atoms, which may be substituted by one or more radicals R 3 , or a combination of these systems, where two or more adjacent substituents R 1  may optionally form a monocyclic or polycyclic, aliphatic, aromatic or heteroaromatic ring system, which may be substituted by one or more radicals R 3 ; 
         R 2  is selected on each occurrence, identically or differently, from the group consisting of a straight-chain alkyl group having 1 to 40 C atoms or a branched or cyclic alkyl group having 3 to 40 C atoms, each of which may be substituted by one or more radicals R 3 , where one or more non-adjacent CH 2  groups may be replaced by R 3 C═CR 3 , C≡C or C═O and where one or more H atoms may be replaced by D, F, Cl, Br, I, CN or NO 2 , an aromatic or heteroaromatic ring system having 5 to 60 aromatic ring atoms, which may in each case be substituted by one or more radicals R 3 , or a combination of these systems; R 1  and R 2  which are adjacent to one another in the 1,2-position may optionally form a monocyclic or polycyclic, aliphatic, aromatic or heteroaromatic ring system, which may be substituted by one or more radicals R 3 ; 
         R 3  is selected from the group consisting of H, D, F, CN, an aliphatic hydrocarbon radical having 1 to 20 C atoms, an aromatic or heteroaromatic ring system having 5 to 30 aromatic ring atoms, in which one or more H atoms may be replaced by D, F, Cl, Br, I or CN, where two or more adjacent substituents R 3  may form a mono- or polycyclic, aliphatic, aromatic or heteroaromatic ring system with one another; 
         n is 1 to 10; 
         m is 1 if L is a single bond or a divalent group, or is 2 if L is a trivalent group, or is 3 if L is a tetravalent group; 
         q is on each occurrence, identically or differently, 0 or 1; 
         the following compounds are excluded from the invention: 
       
       
         
           
           
               
               
           
         
         
           
           
               
               
           
         
         or a compound of the formula (39), 
       
       
         
           
           
               
               
           
         
         wherein t is 1 to 10. 
       
     
     
       13. An electronic device which comprises the compound according to  claim 12 . 
     
     
       14. A process for the preparation of the compound according to  claim 12  which comprises reacting an ortho-diamino-substituted aromatic compound, in which the amino groups are unsubstituted or monosubstituted, with an aromatic phosphonyl chloride derivative or an aromatic oligophosphonyl chloride derivative. 
     
     
       15. An oligomer, polymer or dendrimer containing one or more compounds according to  claim 12 , where one or more bonds are present from the compound to the polymer, oligomer or dendrimer,
 or an oligomer or polymer of the formula (37) or formula (38): 
 
       
         
           
           
               
               
           
         
         where symbols used have the meanings indicated in  claim 12 , and r stands for an integer between 2 and 1,000,000. 
       
     
     
       16. The electronic device according to  claim 1 , wherein Ar 1  stands, identically or differently on each occurrence, for benzene, pyridine, pyrimidine, pyridazine, pyrazine, triazine, furan, thiophene, pyrrole, naphthalene, phenanthrene, quinoline, isoquinoline, quinoxaline, indole, benzofuran, benzothiophene or carbazole. 
     
     
       17. The electronic device according to  claim 1 , wherein R 2  is selected, identically or differently on each occurrence, phenyl, naphthyl, biphenyl or terphenyl, each of which may be substituted by one or more radicals R 3 . 
     
     
       18. The electronic device according to  claim 1 , wherein the following applies to the symbols and indices:
 Ar 1  is, identically or differently on each occurrence, an aryl or heteroaryl group having 6 aromatic ring atoms; 
 Y is on each occurrence, identically or differently, P(═O) or P(═S); 
 Z is, identically or differently on each occurrence, N—R 2  if it does not form a ring of the formula (7) with A or B; 
 X stands for CR 1  or N, where a maximum of one symbol X stands for N; 
 Ar is, identically or differently, an aromatic or heteroaromatic ring system having 5 to 24 aromatic ring atoms; and, none of the aryl or heteroaryl groups of the aromatic or heteroaromatic ring system contains more than 10 aromatic ring atoms; 
 q is 0; 
 n is 1, 2 or 3; 
 R 1  is selected, identically or differently on each occurrence, from the group consisting of H, D, F, CN, N(R 3 ) 2 , a straight-chain alkyl or alkoxy group having 1 to 20 C atoms or a branched or cyclic alkyl or alkoxy group having 3 to 20 C atoms or an alkenyl group having 2 to 20 C atoms, each of which may be substituted by one or more radicals R 3 , where one or more non-adjacent CH 2  groups may be replaced by R 3 C═CR 3  or O and where one or more H atoms may be replaced by D or F, an aromatic or heteroaromatic ring system having 5 to 30 aromatic ring atoms, which may in each case be substituted by one or more radicals R 3 , an aryloxy or heteroaryloxy group having 5 to 30 aromatic ring atoms, which may be substituted by one or more radicals R 3 , or a combination of these systems, where two or more adjacent substituents R 1  may optionally form a monocyclic or polycyclic, aliphatic, aromatic or heteroaromatic ring system, which may be substituted by one or more radicals R 3 ; 
 R 2  is selected on each occurrence, identically or differently, from the group consisting of a straight-chain alkyl group having 1 to 10 C atoms or a branched or cyclic alkyl group having 3 to 10 C atoms, each of which may be substituted by one or more radicals R 3 , where one or more atoms may be replaced by F or D, an aromatic or heteroaromatic ring system having 5 to 30 aromatic ring atoms, which may in each case be substituted by one or more radicals R 3 , or a combination of these systems; R 1  and R 2  which are adjacent to one another in the 1,2-position may optionally form a monocyclic or polycyclic, aliphatic, aromatic or heteroaromatic ring system, which may be substituted by one or more radicals R 3 ; 
 the other symbols and indices have the meanings indicated in  claim 1 . 
 
     
     
       19. The electronic device according to  claim 1 , wherein the following applies to the symbols and indices used:
 Ar 1  is selected, identically or differently on each occurrence, from the group consisting of benzene, pyridine, pyrimidine, pyridazine, pyrazine, triazine, furan, thiophene, pyrrole, naphthalene, quinoline, isoquinoline, quinoxaline, indole, benzofuran, benzothiophene and carbazole; 
 Y is P(═O); 
 Z is, identically or differently on each occurrence, N—R 2  if it does not form a ring of the formula (7) with A or B; 
 X is, identically or differently on each occurrence, CR 1 ; 
 Ar is an aromatic or heteroaromatic ring system having 5 to 24 aromatic ring atoms, which is built up from in each case one or more of the groups benzene, pyridine, pyrimidine, pyridazine, pyrazine or triazine; 
 q is 0; 
 n is 1 or 2; 
 R 1  is selected, identically or differently on each occurrence, from the group consisting of H, D, F, CN, a straight-chain alkyl group having 1 to 4 C atoms, or a branched or cyclic alkyl group having 3 to 5 C atoms, or an alkenyl group having 2 to 4 C atoms, each of which may be substituted by one or more radicals R 3 , where one or more H atoms may be replaced by I), an aromatic or heteroaromatic ring system having 5 to 12 aromatic ring atoms, which may in each case be substituted by one or more radicals R 3 , or a combination of these systems, where two or more adjacent substituents R 1  may optionally form a monocyclic or polycyclic, aliphatic, aromatic or heteroaromatic ring system, which may be substituted by one or more radicals R 3 ; 
 R 2  is selected on each occurrence, identically or differently, from the group consisting of an aromatic or heteroaromatic ring system having 5 to 24 aromatic ring atoms, which may in each case be substituted by one or more radicals R 3 ; 
 the other symbols and indices used have the meanings indicated in  claim 1 . 
 
     
     
       20. The electronic device according to  claim 10 , wherein the phosphorescent emitter employed is a compound which contains iridium or platinum. 
     
     
       21. The electronic device according to  claim 1 , wherein
 R 1  is selected on each occurrence, identically or differently, from the group consisting of H, D, F, Cl, Br, I, CN, NO 2 , N(R 3 ) 2 , C(═O)R 3 , a straight-chain alkyl, alkoxy or thioalkyl group having 1 to 40 C atoms or a branched or cyclic alkyl, alkoxy or thioalkyl group having 3 to 40 C atoms or an alkenyl or alkynyl group having 2 to 40 C atoms, each of which may be substituted by one or more radicals R 3 , where one or more non-adjacent CH 2  groups may be replaced by R 3 C═CR 3 , C≡C, Si(R 3 ) 2 , Ge(R 3 ) 2 , Sn(R 3 ) 2 , C═O, C═S, C═Se, C═NR 3 , P(═O)(R 3 ), SO, SO 2 , NR 3 , O, S or CONR 3  and where one or more H atoms may be replaced by D, F, Cl, Br, I, CN or NO 2 , an aromatic or heteroaromatic ring system having 5 to 60 aromatic ring atoms, which may in each case be substituted by one or more radicals R 3 , an aryloxy or heteroaryloxy group having 5 to 60 aromatic ring atoms, Which may be substituted by one or more radicals R 3 , or a combination of these systems; 
 R 2  is selected on each occurrence, identically or differently, from the group consisting of a straight-chain alkyl group having 1 to 40 C atoms or a branched or cyclic alkyl group having 3 to 40 C atoms, each of which may be substituted by one or more radicals R 3 , where one or more non-adjacent CH 2  groups may be replaced by R 3 C═CR 3 , C≡C or C═O and where one or more H atoms may be replaced by D, F, Cl, Br, I, CN or NO 2 , an aromatic or heteroaromatic ring system having 5 to 60 aromatic ring atoms, which may in each case be substituted by one or more radicals R 3 , or a combination of these systems; and 
 R 3  is selected from the group consisting of H, D, F, CN, an aliphatic hydrocarbon radical having 1 to 20 C atoms, an aromatic or heteroaromatic ring system having 5 to 30 aromatic ring atoms, in which one or more H atoms may be replaced by D, F, Cl, Br, I or CN. 
 
     
     
       22. The compound according to  claim 12 , wherein
 R 1  is selected on each occurrence, identically or differently, from the group consisting of H, D, F, Cl, Br, I, CN, NO 2 , N(R 3 ) 2 , C(═O)R 3 , a straight-chain alkyl, alkoxy or thioalkyl group having 1 to 40 C atoms or a branched or cyclic alkyl, alkoxy or thioalkyl group having 3 to 40 C atoms or an alkenyl or alkynyl group having 2 to 40 C atoms, each of which may be substituted by one or more radicals R 3 , where one or more non-adjacent CH 2  groups may be replaced by R 3 C═CR 3 , C≡C, Si(R 3 ) 2 , Ge(R 3 ) 2 , Sn(R 3 ) 2 , C═O, C═S, C═Se, C═NR 3 , P(═O)(R 3 ), SO, SO 2 , NR 3 , O, S or CONR 3  and where one or more H atoms may be replaced by D, F, Cl, Br, I, CN or NO 2 , an aromatic or heteroaromatic ring system having 5 to 60 aromatic ring atoms, which may in each case be substituted by one or more radicals R 3 , an aryloxy or heteroaryloxy group having 5 to 60 aromatic ring atoms, which may be substituted by one or more radicals R 3 , or a combination of these systems; 
 R 2  is selected on each occurrence, identically or differently, from the group consisting of a straight-chain alkyl group having 1 to 40 C atoms or a branched or cyclic alkyl group having 3 to 40 C atoms, each of which may be substituted by one or more radicals R 3 , where one or more non-adjacent CH 2  groups may be replaced by R 3 C═CR 3 , C≡C or C═O and where one or more atoms may be replaced by D, F, Cl, Br, I, CN or NO 2 , an aromatic or heteroaromatic ring system having 5 to 60 aromatic ring atoms, which may in each case be substituted by one or more radicals R 3 , or a combination of these systems; and 
 R 3  is selected from the group consisting of H, D, F, CN, an aliphatic hydrocarbon radical having 1 to 20 C atoms, an aromatic or heteroaromatic ring system having 5 to 30 aromatic ring atoms, in which one or more H atoms may be replaced by D, F, Cl, Br, I or CN.